The goals of the research is to determine the structure of eukaryotic ribosomes. The endeavor is motivated by a desire to provide a rational account of the biochemistry underlying the function of the organelle in protein synthesis. It is by no means certain, perhaps not even likely, that knowledge of the structure will lead parri passu to an understanding of the function of ribosomes. However, it is difficult to imagine being able to describe function in molecular detail without knowledge of the structure it is obvious that a requisite is the sequences of nucleotides and of amino acids in the constituent nucleic acids and proteins. A commitment has been made both to the structure of the particle. At any rate, if one has undertaken to attempt to solve the structure it is obvious that a requisite is the sequences of nucleotides and of amino acids in the constituent nucleic acids and proteins. A commitment has been made both to the large enterprise, i.e to the solution of the structure of mammalian (rat) ribosomes, and to the acquisition of the chemical data. The covalent structure of the four species of RNA has been established. Eighty-two proteins have been isolated from the particles and the sequences of amino acids in 28 have been determined either directly or they have been deduced from the sequence of nucleotides in recombinant cDNAs. The specific aim (1) is to continue of determine the sequences of amino acids in rat ribosomal proteins by a combination to determine the sequences of amino acids in rat ribosomal proteins by a combination of protein chemistry and recombinant DNA technology. In addition we shall (2) determine the structure and the organization of the genes for a selected few ribosomal proteins, P0, P1, and P2 ( the P proteins) and L5. Finally we plan (3) to attempt to determine the relationship of the structure of the cytotoxic protein ricin to its action in activation ribosomes. The determination of these sequences is a contribution to a set of data which it is hoped will eventually encompass the structure of all the proteins in the ribosomes of this mammalian species. The primary motivation for the accumulation of this data is the value it must have in arriving at a solution of the structure of the organelle. However, the information of the proteins, in defining the rules that govern the interaction of the proteins and the rRNAs, and in uncovering the amino acid sequences that direct the protein to the nucleolus for assembly on nascent rRNA.